[PATCH v4 00/14] KVM: arm64: Introduce kvm_{un}share_hyp()

[Quentin Perret]

Hi all,

This is v4 of the series previously posted here:

  https://lore.kernel.org/kvmarm/20211201170411.1561936-1-qperret@google.com/

This series implements an unshare hypercall at EL2 in nVHE protected
mode, and makes use of it to unmmap guest-specific data-structures from
EL2 stage-1 during guest tear-down. Crucially, the implementation of the
share and unshare routines use page refcounts in the host kernel to
avoid accidentally unmapping data-structures that overlap a common page.

This series has two main benefits. Firstly it allows EL2 to track the
state of shared pages cleanly, as they can now transition from SHARED
back to OWNED. This will simplify permission checks once e.g. pkvm
implements a donation hcall to provide memory to protected guests, as
there should then be no reason for the host to donate a page that is
currently marked shared. And secondly, it avoids having dangling
mappings in the hypervisor's stage-1, which should be a good idea from
a security perspective as the hypervisor is obviously running with
elevated privileges. And perhaps worth noting is that this also
refactors the EL2 page-tracking checks in a more scalable way, which
should allow to implement other memory transitions (host donating memory
to a guest, a guest sharing back with the host, ...) much more easily in
the future.

Changes since v3:
 - fixed refcount of hyp stage-1 page-table pages when only changing SW
   bits (Will)
 - misc minor cleanups (Will, Andrew)
 - rebased on kvmarm/next

Quentin Perret (6):
  KVM: arm64: Provide {get,put}_page() stubs for early hyp allocator
  KVM: arm64: Refcount hyp stage-1 pgtable pages
  KVM: arm64: Fixup hyp stage-1 refcount
  KVM: arm64: Introduce kvm_share_hyp()
  KVM: arm64: pkvm: Refcount the pages shared with EL2
  KVM: arm64: pkvm: Unshare guest structs during teardown

Will Deacon (8):
  KVM: arm64: Hook up ->page_count() for hypervisor stage-1 page-table
  KVM: arm64: Implement kvm_pgtable_hyp_unmap() at EL2
  KVM: arm64: Extend pkvm_page_state enumeration to handle absent pages
  KVM: arm64: Introduce wrappers for host and hyp spin lock accessors
  KVM: arm64: Implement do_share() helper for sharing memory
  KVM: arm64: Implement __pkvm_host_share_hyp() using do_share()
  KVM: arm64: Implement do_unshare() helper for unsharing memory
  KVM: arm64: Expose unshare hypercall to the host

 arch/arm64/include/asm/kvm_asm.h              |   1 +
 arch/arm64/include/asm/kvm_host.h             |   2 +
 arch/arm64/include/asm/kvm_mmu.h              |   2 +
 arch/arm64/include/asm/kvm_pgtable.h          |  21 +
 arch/arm64/kvm/arm.c                          |   6 +-
 arch/arm64/kvm/fpsimd.c                       |  36 +-
 arch/arm64/kvm/hyp/include/nvhe/mem_protect.h |   6 +
 arch/arm64/kvm/hyp/nvhe/early_alloc.c         |   5 +
 arch/arm64/kvm/hyp/nvhe/hyp-main.c            |   8 +
 arch/arm64/kvm/hyp/nvhe/mem_protect.c         | 500 +++++++++++++++---
 arch/arm64/kvm/hyp/nvhe/setup.c               |  22 +-
 arch/arm64/kvm/hyp/pgtable.c                  | 102 +++-
 arch/arm64/kvm/mmu.c                          | 137 ++++-
 arch/arm64/kvm/reset.c                        |  10 +-
 14 files changed, 739 insertions(+), 119 deletions(-)

-- 
2.34.1.173.g76aa8bc2d0-goog